Because the microstructure consists of constituents with strong differences in their mechanical properties, dual phase steels exhibit remarkably high-energy absorption along with an excellent combination of strength and ductility. Under the circumstances in which modern sheet metal forming processes, involving complicated load paths, are applied, different deformation mechanisms in the heterogeneous microstructure need to be taken into account. With the help of the micromechanical modeling approach that considers the influence of microstructural features on the mechanical response of materials, this demand can be well met.
This study proposes a micromechanical modeling scheme to investigate the influence of the microstructure of DP600 steel on the sheet metal forming process. This study can be divided into two parts which are prediction of the mechanical response under various loading conditions by means of microstructure-based simulations and investigation of microstructure changes during the sheet metal forming process. In the first part, microstructure of DP600 steel is quantitatively characterized using the EBSD analysis to gain relevant statistical information of all important microstructural features such as phase volume fractions and grain size distributions and orientation distributions of each constituent. The obtained results are then used to generate the microstructure model with the help of an advanced dynamic microstructure generator (ADMG), which combines a particle simulation method with radical Voronoi tessellation to construct proper grain size and orientation distributions. Finite element simulations with a non-local crystal plasticity model for the individual grains are then conducted under tension and reversed shear. With the help of these simulations, crystal plasticity parameters are adapted to match the experiments. The resulting parameterized microstructure model of DP600 steel is then applied to various loading conditions to investigate the corresponding mechanical responses. For the second part, macroscopic simulations of the bending process are performed and local deformation fields of the location of interest are captured and imposed as boundary conditions on the microstructure model to study changes in the microstructural features such grain shape and texture. Finally, the influence of microstructural features on deformation mechanisms is studied.